Bimetallic casting

ABSTRACT

A method of forming a casting includes providing a preform to a mold cavity. The preform is formed from one of a first metal and a second metal and defines an interface surface. A molten portion of the other of the first metal and the second metal is cast into the mold such that the molten portion proximately contacts the interface surface of the preform. An interface layer at the interface surface, a first portion defined by the mold cavity and the interface layer, and a second portion defined by the interface layer, are formed during casting. The interface layer may define a metallurgical bond between the first portion and the second portion. In the non-limiting example provided herein, the first portion is substantially comprised of aluminum and the second portion is substantially comprised of magnesium. In a non-limiting example, the casting may be configured as a vehicle wheel.

TECHNICAL FIELD

The present invention relates to forming a bimetallic casting.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. patent application Ser. No.12/902,370 filed on Oct. 12, 2010, which is hereby incorporated byreference in its entirety.

BACKGROUND

Components formed of magnesium offer advantages such as high strength toweight ratio when compared to similarly sized components formed ofaluminum or ferrous based materials. For example, wheels have beenforged from magnesium for specialized applications such as racingvehicle wheels. The use of magnesium wheels for non-specialty vehicleshas been limited by the poor corrosion performance of magnesium.Coatings applied to the surface of magnesium components, for example,diffused aluminum powder coatings, to improve the corrosion performanceof the magnesium have been developed, however spalling and chipping ofapplied coatings negates the protective effect of the coating. Thematerial, processing time, equipment, handling and transportation, andassociated costs required to apply coatings such as diffused aluminumpowder coatings to magnesium components in a secondary process aredisadvantageous to the use of applied coatings for corrosion improvementof magnesium components.

SUMMARY

A method of forming a casting is provided. The casting is comprised ofan interface layer, a first portion defined by a mold cavity and theinterface layer, and a second portion defined by the interface layer.The casting may be configured, in a non-limiting example, as a wheeladaptable for use on a vehicle. The method includes providing a preformto a mold cavity, wherein the mold cavity is defined by a casting mold.The preform is formed from one of a first metal and a second metal andis configured to define an interface surface. A molten portion of theother of the first metal and the second metal is provided to the moldcavity, and is cast into the mold such that the molten portionproximately contacts the interface surface of the preform. The methodincludes forming a casting which includes an interface layer at theinterface surface, a first portion defined by the mold cavity and theinterface layer; and a second portion defined by the interface layer.The interface layer may include a metallurgical bond formed between thefirst portion and the second portion. In the non-limiting exampleprovided herein, the first portion is substantially comprised ofaluminum or an aluminum alloy, and the second portion is substantiallycomprised of magnesium or a magnesium alloy.

The method may provide a casting which is adaptable for use as a wheelfor a vehicle and configured such that the aluminum-based first portionsubstantially encapsulates the magnesium-based second portion to providea vehicle wheel with a higher strength to weight ratio in comparison toaluminum alloy wheels, and improved corrosion performance in comparisonto magnesium alloy wheels.

The above features and other features and advantages of the presentinvention are readily apparent from the following detailed descriptionof the best modes for carrying out the invention when taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a cross-sectional view of a moldand a preform defining a second portion of a casting produced by themold;

FIG. 2 is a schematic illustration of a cross-sectional view of a moldand a preform defining a first portion of a casting produced by themold;

FIG. 3 is a plan perspective view of a casting formed using the methodof FIG. 1 or FIG. 2;

FIG. 4 is a schematic cross-sectional view of the casting of FIG. 3;

FIG. 5 is a plan perspective view of a wheel formed using the method ofFIG. 1 or FIG. 2; and

FIG. 6 is a schematic cross-sectional view of the wheel of FIG. 5.

DETAILED DESCRIPTION

Referring to the drawings wherein like reference numbers represent likecomponents throughout the several figures. The elements shown in FIGS.1-6 are not to scale or proportion. Accordingly, the particulardimensions and applications provided in the drawings presented hereinare not to be considered limiting.

FIG. 1 shows a cross-sectional view of a casting mold 10, which definesa mold cavity 16 and a sprue or gate 14, through which molten metal 12may be provided to the mold cavity 16 during the casting process. Themold 10 may be a permanent mold, a sand mold or other mold suitable forcasting a cast component as described herein. The mold 10 may furtherinclude additional gates, runners and core pieces configured andpositioned as may be required to provide molten metal to the mold cavity16 in sufficient quantity and at a suitable flow, distribution andtemperature to produce a casting as described herein.

A method of forming a casting is provided, and is shown in FIGS. 1 and2. In FIG. 1, the method includes providing a preform or insert 20 tothe mold cavity 16. In the non-limiting example shown, the mold cavity16 is generally configured to define a wheel or wheel blank which isadaptable for use on a vehicle (see FIGS. 3-4 and 5-6). The preform 20is formed from a first metal, which in the example shown in FIG. 1 maybe magnesium, a magnesium alloy, or a material of predominantlymagnesium composition.

The preform 20 is configured to define an interface surface 22, and maybe formed as one of a casting, a forging, an extrusion, a stamping and aspun component. The preform 20 is positioned in the mold cavity 16 suchthat a passage 18 is defined between the interface surface 22 and theinner surface of the mold cavity 16. The passage 18 defines the castportion of the component produced by casting metal 12 into the moldcavity 16 of FIG. 1, where the cast portion is shown in FIG. 4 as afirst portion 53 of a cast component 50 generally configured as a wheelor wheel blank and produced using the casting method of FIG. 1. Thepreform 20 may be positioned in the mold cavity 16, for example, by corepins 15 or similar locating elements, to locate the preform 20 in thecavity 16 and to allow for the molten metal 12 to flow around thepreform 20 during casting. The core pins 15 may be located in the moldcavity and in proximate contact with areas of the preform 20 which arenon-critical or less critical to the corrosion performance of thefinished casting. The non-critical or less critical areas may be areasof the casting which have limited exposure to corrosive elements duringuse, or which may be provided protection from corrosive elements byanother component of the wheel assembly. For example, the preform 20 maybe positioned in mold cavity 16 using core pins 15 in proximate contactwith a hub surface, generally defined by section D in FIG. 1, where thehub surface of the cast wheel may be protected by a wheel cover or othertrim piece when the wheel is in its as-installed configuration on avehicle. It would be understood that mold cavity 16 may be provided withadditional core pins or locating elements in other areas or inconfigurations other than those shown in FIG. 1.

The passage 18 is characterized by a gap between the interface surface22 and the adjacent surface of the mold cavity 16, where the width ofthe gap is indicated at various sections thereof in FIG. 1 by theletters A, B, C, D and E. It is understood that the width of the gapbetween the interface surface 22 of preform 20 and the wall of the moldcavity 16 will generally define the thickness of the cast portion formedby metal 12 in FIG. 1 and generally the thickness of the first portion53 of the cast component 50 shown in FIGS. 3 and 4. The configuration ofpassage 18 and the width of the gap defined by passage 18 is determinedby the configuration of the interface surface 22 of preform 20 and theposition of preform 20 in mold cavity 16, wherein a change in either orboth of these will change the configuration of passage 18 and theresultant thickness of the cast portion formed by molten metal 12.

A molten portion of another, or second, metal 12 is provided to the moldcavity 16 through the sprue 14, and is cast into the mold cavity 16 suchthat the molten portion of the metal 12 flows into and through thepassage 18 and proximately contacts the interface surface 22 of thepreform 20. In the non-limiting example shown in FIG. 1 the second metal12 may be one of aluminum, an aluminum alloy or a material ofpredominantly aluminum composition. The molten portion 12 solidifies todefine the first portion 53 generally surrounding a second portion 55 ofa cast component 50 (see FIGS. 3 and 4), where the second portion 55 isgenerally defined by and comprises the preform 20. The preform 20 may beoperatively configured as a heat sink, such that preform 20 absorbs anddissipates heat generated by the molten metal 12 as metal 12 solidifiesto form the first portion 53 and the interface layer 52.

The method includes forming an interface layer (see 52 in FIG. 4, forexample) at the interface surface 22 during the casting process. Theinterface layer 52 may form as the molten metal 12 contacts theinterface surface 22 of the preform 20, which may cause some degree ofmelting of the preform 20 at the interface 22. In the example shown, themelting temperature of the molten metal 12, e.g., the aluminum or analuminum alloy, is similar to the melting temperature of the magnesiumor magnesium alloy comprising preform 20. The resultant interface layer52 which is formed during the casting process may define a metallurgicalbond between the first portion 53 and the second portion 55 of casting50, and may further be defined by an intermetallic compound formed atthe interface layer 52, where the intermetallic compound includes, forexample, magnesium and aluminum.

The passage 18 may be defined by a gap of constant width, e.g., thedistances A, B, C, D, E may be substantially equal, such that the castportion formed by metal 12 is of substantially equal thickness in eachsection and across the surface of the casting 50. The gap may be ofvariable width, e.g., the distances or gap widths A, B, C, D, E may notall be equal, such that the thickness of the cast portion is variableacross the surface of the casting 50 or from one section to anothersection. The gap width may be varied, for example, to provide a firstportion 53 (see FIG. 3) of variable thickness on wheel casting 50. Forexample, thicker sections of aluminum may be provided on certain areasof the wheel 50 for increased corrosion protection, or to provideadditional stock for subsequent machining or other finishing treatments.For example, it may be desirable to configure passage 18 such that thegap width C is greater than the gap widths B and D, wherein the castsections defined by gap width C are on the wheel face, which, when thewheel is assembled on a vehicle, is exposed to a road environmentincluding stone chipping, road dirt, water, salt and other factors fromwhich corrosion protection is required. By comparison, gap widths B andD corresponds to sections of the wheel 50 which may be substantiallycovered by a vehicle tire and a hub cap or decorative trim cover,respectively, such that these sections may be minimally exposed to theroad environment. Accordingly, it may be desirable to minimize the gapwidths B and D such that the aluminum portion 53 in these areas providesnominal corrosion protection to the magnesium portion 55 of the wheel(referring to FIG. 3), and recognizing aluminum is denser thanmagnesium, to minimize the weight contribution of the aluminum portionof the wheel to maximize the strength to weight ratio of the wheel 50.By way of another non-limiting example, the gap width E may be greaterthan the gap width of one or more of the other sections, to provide anincreased thickness of aluminum at the rim of the wheel, for additionalcorrosion protection against nicks and scratches and stone-impingementon the protruding edge, and/or to provide additional material for finishof the bead mounting surface by machining or other secondary processes.

The mold cavity 16 and the passage 18 may be configured, as shown inFIG. 1, such that molten metal 12 can be poured into mold 10 tosubstantially or fully surround the preform 20, such that metal 12encapsulates the surface of the preform 20 during the casting process.The casting produced, shown in a non-limiting example as casting 50 inFIGS. 3 and 4, may be characterized by a first portion 53 whichsubstantially encapsulates the second portion 55, such that the aluminumcomprising the first portion 53 provides a continuous, substantiallyuninterrupted corrosion protection layer over the magnesium comprisingthe second portion 55, thus coating or sealing the magnesium to limitingthe exposure of the second portion 55 to corrosive factors andenvironments, thereby improving the corrosion performance of the wheel50.

FIG. 2 shows a cross-sectional view of an alternate arrangement for acasting process to produce, for example, the cast wheel 50 shown inFIGS. 3 and 4. FIG. 2 shows a casting mold 30, which defines a moldcavity 36, and a sprue or gate 34, through which molten metal 32 may beprovided to the mold cavity 36 during the casting process. The mold 30may be a permanent mold, a sand mold or other mold suitable for castinga cast component as described herein. The mold 30 may further includeadditional gates and runners as may be required to provide molten metalto the mold cavity 36 in sufficient quantity and at a suitable flow,distribution and temperature to produce a casting as described herein.

A method of forming a casting is provided, and includes providing apreform or insert 40 to the mold cavity 36. In the non-limiting exampleshown, the mold cavity 36 is generally configured to define a wheel orwheel blank which is adaptable for use on a vehicle (see FIGS. 3-4 and5-6). The preform 40 is formed from a first metal, which in the exampleshown in FIG. 2 may be aluminum, an aluminum alloy, or material ofpredominantly aluminum composition.

The preform 40 is configured to define an interface surface 22, and maybe positioned in mold cavity 36 such that the outermost surface ofpreform 40 generally conforms to the inner surface of mold cavity 36.The preform 40 may be configured to provide a passage 38, which isdefined by the interface surface 22 of the preform 40. The passage 38may be described as a preform cavity, a chamber, and/or a hollow spacedefined by the preform 40. The mold 30 and the preform 40 are configuredsuch that molten metal 32 may be cast into the passage 38, such that thepassage 38 and/or interface surface 22 defines the cast portion of thecomponent produced by casting metal 32 into the mold cavity 36. The castportion comprising metal 32 is shown in FIG. 4 as a second portion 55 ofa cast component 50 generally configured as a wheel or wheel blank andproduced using the casting method of FIG. 2.

The preform 40 is characterized by a width or thickness defined by theinterface surface 22 and the outermost surface of preform 40, which maybe configured to generally conform to the inner surface of mold cavity36, where the width or thickness of the preform 40 is indicated atvarious sections thereof in FIG. 2 by the letters A, B, C, D and E. Itis understood that the thickness of preform 40 between the interfacesurface 22 of preform 40 and the outermost surface of preform 40 willgenerally define the thickness of the first portion 53 of the component50 shown in FIGS. 3 and 4. The configuration of passage 38 and thesection thickness defined by preform 40 is determined by theconfiguration of the interface surface 22 of preform 40, and theconfiguration of the outermost surface of preform 40, which may conformgenerally to the inner surface of mold cavity 36.

A molten portion of another, or second, metal 32 is provided to the moldcavity 36 through the sprue 34, and is cast into the mold cavity 36 suchthat the molten portion of metal 32 flows into and through the passage38 and proximately contacts the interface surface 22 of the preform 40.In the non-limiting example shown in FIG. 2 the second metal 32 may beone of magnesium, a magnesium alloy, or material of predominantlymagnesium composition. The molten portion 32 solidifies to define asecond portion 55 which is generally surrounded by a first secondportion 53 of a cast component 50 (see FIGS. 3 and 4), where the firstportion 53 is generally defined by and comprises the preform 40.

The method includes forming an interface layer (see 52 in FIG. 4, forexample) at the interface surface 22 during the casting process. Theinterface layer 52 may form as the molten metal 32 contacts theinterface surface 22 of the preform 40, which may cause some degree ofmelting of the preform 40 at the interface 22. In the example shown, themelting temperature of the molten metal 32, e.g., the magnesium ormagnesium alloy, is similar to the melting temperature of the aluminumor an aluminum alloy comprising preform 40. The resultant interfacelayer 52 which is formed during the casting process may define ametallurgical bond between the first portion 53 and the second portion55 of the component 50, and may further be defined by an intermetalliccompound formed at the interface layer 52, where the intermetalliccompound includes, for example, magnesium and aluminum.

The preform 40 may be defined by a constant thickness, e.g., the widthsor thicknesses A, B, C, D, E may be substantially equal, such that thefirst portion 53 defined by preform 40 is of substantially equalthickness in each section across the surface of the cast component 50.The preform 40 may be of varying thickness from section to section,e.g., the thickness or widths A, B, C, D, E may not all be equal, suchthat the thickness of the preform 40 and the thickness of the firstportion 53 defined by preform 40 is variable across the surface of thecasting 50 or from section to section. The thickness may be varied, forexample, to provide a first portion 53 (see FIG. 3) of variablethickness on wheel casting 50. For example, thicker sections of aluminummay be provided on certain areas of the wheel 50 for corrosionperformance or to provide additional material for subsequent machiningor finishing treatments. For example, the section thickness E may begreater than the gap width of one or more of the other sections, toprovide an increased thickness of aluminum at the rim of the wheel, toprovide surplus material to form or finish the bead or tire mountingsurface, and/or for additional corrosion protection against nicks andscratches and stone-impingement on this protruding edge. By way ofanother non-limiting example, it may be desirable to configure preform40 such that the section thickness C is greater than the sectionthicknesses B and D, wherein the sections of first portion 53 defined bythickness C are on the wheel face, which, when the wheel is assembled ona vehicle, is exposed to a road environment including stone chipping,road dirt, water, salt and other factors from which corrosion protectionis required. By comparison, section thicknesses B and D correspond tosections of the wheel 50 which may be substantially covered by a vehicletire and a hub cap or decorative trim cover, respectively, such thatthese sections may be minimally exposed to the road environment.Accordingly, it may be desirable to minimize the section thicknesses Band D such that the aluminum portion 53 in these areas provides nominalcorrosion protection to the magnesium portion 55 of the wheel (referringto FIG. 3), and recognizing that aluminum is denser than magnesium, tominimize the weight contribution of the aluminum portion of the wheel tomaximize the strength to weight ratio of the wheel 50. For example,section thickness B may be configured to be minimized such that duringthe casting process the molten metal 32 provides sufficient heattransfer to section B such that section B is at least partially meltedand metal 32 significantly diffuses with the metal of preform 40 to forman intermetallic compound at the surface of casting 50 in the area ofsection B produced by the casting method shown in FIG. 2.

The mold cavity 36 and the preform 40 may be configured, as shown inFIG. 2, such that preform 40 may significantly encapsulate the castsecond portion 55. By “significantly” encapsulating the second portion55, the preform 40 may encapsulate all but an insignificant area of thesurface of the second portion 55. The mold 30, mold cavity 36 andpreform 40 may be configured such that the non-encapsulated area isgenerally located in a section of the wheel 50 which may be providedprotection from corrosive elements by another component, for example, ahub or wheel cover or decorative trim piece, or which is located in anarea of the wheel 50 which has limited exposure to road contaminantssuch as salt and water, stone impingement, or other environmentalfactors from which corrosion protection may be desired. The casting 50may be characterized by a first portion 53 which significantlyencapsulates the second portion 55, such that the aluminum comprisingfirst portion 53 defines or provides a corrosion protection layer whichsubstantially covers the magnesium comprising the second portion 55,thus limiting the exposure of the magnesium-based material comprisingthe second portion 55 to corrosive factors and environments, therebyimproving the corrosion performance of the wheel 50.

The preform 40 may be formed as one of a casting, a forging, anextrusion, a stamping and a spun component or may be comprised of two ormore preform elements, which may be operatively attached to one another.In a non-limiting example, the preform 40 may be formed by casting thepreform 40 in the mold cavity 36 of mold 30. In this configuration, themetal comprising preform 40, which may be aluminum or an aluminum alloy,is provided in a molten state to the mold cavity 36 and as would beunderstood is cast to form the preform 40 including the preform passage38.

FIG. 3 shows an example casting 50 which may be produced using a methodas shown in FIG. 1 or FIG. 2. FIG. 4 shows a cross-sectional schematicview of the casting 50 taken through a section 4-4 shown in FIG. 3 andgenerally corresponding to the cross-sectional view of the casting moldshown in FIG. 1 and FIG. 2. In a non-limiting example, the casting 50may be generally configured as a wheel or wheel blank adaptable for usein a vehicle. The wheel 50 includes a first portion 53 made of a firstmetal, a second portion 55 made of a second metal and an interface layer52 defining a metallurgical bond between the first portion 53 and thesecond portion 55. The first portion 53 may be referred to as the shellor shell portion, and the second portion 55 may be referred to as thecore or core portion. In a non-limiting example, the first portion 53may be substantially comprised of aluminum, an aluminum alloy or amaterial of predominantly aluminum composition, and the second portion55 may be substantially comprised of magnesium, a magnesium alloy or amaterial of predominantly magnesium composition to produce a wheel 50which may be defined by a high strength to weight ratio. The interfacelayer 52 may further be defined by an intermetallic compound formed atthe interface layer 52 during the casting process by which wheel 50 isformed, where the intermetallic compound includes, for example,magnesium and aluminum.

In a first configuration, the wheel 50 may be produced using the castingmethod shown in FIG. 1, wherein the first portion 53 is defined by acast portion comprising metal 12, and is further defined by an interfacelayer 52 and the outermost or exterior surface of wheel 50 whichgenerally conforms to the mold cavity 16. In the first configuration,the second portion 55 is defined by the preform portion 20 and theinterface layer 52. In a second configuration, the wheel 50 may beproduced using the casting method shown in FIG. 2, wherein the firstportion 53 is defined by the preform portion 40 and the interface layer52, and the second portion 55 is defined by a cast portion comprisingmetal 32 and defined by the interface layer 52, as described previouslyfor FIG. 2.

It would be understood that multiple configurations of a casting or castcomponent produced as described herein may be possible. For example,FIG. 5 shows another example of a wheel 60 which may be formed using themethod shown in FIG. 1 or FIG. 2. The wheel 60 includes a hub opening orhub bore 59, and further defines multiple openings 57 which may define,for example, spokes of the wheel 60. FIG. 6 shows a cross-sectionalschematic view of the wheel 60 taken through a section 6-6 shown in FIG.5, which illustrates a first portion 53 of the wheel 60 generallydefining the outer surface or shell of the wheel 60, and a secondportion 55 of the wheel 60 generally defining the core or body portionof the wheel 60. The first portion 53 is generally comprised of a firstmetal and the second portion 55 is generally comprised a second metal.An interface layer 52 defines a metallurgical bond between the firstportion 53 and the second portion 55. In a non-limiting example, thefirst portion 53 may be substantially comprised of aluminum, an aluminumalloy or a material of predominantly aluminum composition, and thesecond portion 55 may be substantially comprised of magnesium, amagnesium alloy or a material of predominantly magnesium composition.The interface layer 52 may further be defined by an intermetalliccompound formed at the interface layer 52 during the casting process bywhich wheel 60 is formed, where the intermetallic compound includes, forexample, magnesium and aluminum.

In a first configuration, the wheel 60 may be produced using a castingmethod such as the method shown in FIG. 1, wherein the first portion 53is defined by a cast portion comprising a metal 12. The cast portioncomprising first portion 53 is defined during the forming method shownin FIG. 1 by a preform interface surface 22 and the mold cavity 16. Itwould be understood that the mold cavity 16 shown in FIG. 1, may bemodified to produce the wheel 60 shown in FIGS. 5 and 6, for example, bymodifying the configuration of the mold cavity 16 and/or by the additionof mold elements or features such as mold inserts to define openings 57and bore 59. Further, in the first configuration, the preform which isprovided and which defines second portion 55 of wheel 60 may be modifiedfrom the configuration shown in FIG. 1 to provide, for example, amodified interface surface 22 defining openings 57 and bore 59 of wheel60.

In a second configuration, the wheel 60 may be produced using thecasting method shown in FIG. 2, wherein the first portion 53 is definedby a preform and the interface layer 52, and the second portion 55 isdefined by a cast portion comprising the metal 32 and further defined bythe interface layer 52, as described previously for FIG. 2. It would beunderstood that the mold cavity 36 shown in FIG. 2 may be modified toproduce the wheel 60 shown in FIGS. 5 and 6, for example, by modifyingthe configuration of the mold cavity 36 and/or by the addition of moldelements or features such as mold inserts to define openings 57 and bore59. Further, in the second configuration produced using the method shownin FIG. 2, the preform which is provided and which defines first portion53 of wheel 60 may be modified from the configuration shown in FIG. 2 toprovide, for example, a modified passage configuration, which mayinclude one or more passages, and a modified interface surface orinterface surfaces to define openings 57 and bore 59 of wheel 60. Thesprue and/or gating configuration of mold 30 may also be modified toprovide the molten metal flow and distribution to the passage orpassages defined by the preform, to cast the second portion 55,including, for example, the spokes of wheel 60 defined by openings 57.

The casting and the method of forming described herein are illustratedusing an example of a vehicle wheel as the cast component. The exampleof a vehicle wheel shown in FIGS. 1-6 is intended to be non-limiting.The casting and the method of forming described herein may be configuredto provide other components where a bimetal structure is advantageous,for example, to provide a high strength to weight ratio, or a surfacestructure differentiated from the core structure for corrosionprotection or other functional, appearance, or performancecharacteristics and features. It would be understood that materialcombinations other than aluminum-based and magnesium-based materials arepossible using the methods described herein.

It would be further understood that a cast component produced by amethod as described herein may be modified by additional processingand/or secondary treatment to enhance, optimize and/or develop certaincharacteristics and/or features. Non-limiting examples of additionalprocessing and/or secondary treatments which may be applied or used tomeet dimensional, appearance, function and/or performance requirementsand specifications include machining, burnishing, polishing, pressing,forging, heat treating, anodizing, localized surface treatment such aspeening, laser treatment, friction mixing, etc., or a combinationthereof.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A method of forming a casting, the method comprising: inserting apreform into a mold cavity, wherein the mold cavity is defined by amold; wherein the preform is formed from one of a first metal and asecond metal and is configured to define an interface surface; pouring amolten portion of the other of the first metal and the second metal intothe mold cavity such that the molten portion proximately contacts theinterface surface of the preform to form the casting including: aninterface layer at the interface surface; a first portion defined by themold cavity and the interface layer; and a second portion defined by theinterface layer.
 2. The method of claim 1, wherein the interface layerfurther includes a metallurgical bond formed between the first portionand the second portion.
 3. The method of claim 1, wherein the firstportion is substantially comprised of one of aluminum and an aluminumalloy; and wherein the second portion is substantially comprised of oneof magnesium and a magnesium alloy.
 4. The method of claim 1, whereinthe casting is adaptable for use as a wheel for a vehicle.
 5. The methodof claim 1, wherein the first portion substantially comprises thepreform.
 6. The method of claim 1, wherein the second portionsubstantially comprises the preform.
 7. The method of claim 1, whereinproviding the preform to the mold cavity further includes forming atleast one passage defined by the interface surface of the preform; andwherein providing the molten portion into the mold cavity furtherincludes providing the molten portion into the at least one passage suchthat the second metal in a molten state is in proximate contact with theinterface surface of the preform.
 8. The method of claim 1, wherein theat least one passage is further defined by the mold cavity.
 9. Themethod of claim 1, wherein the first metal is one of an aluminum alloyand a magnesium alloy; and wherein the second metal is the other of analuminum alloy and a magnesium alloy.
 10. The method of claim 1, whereinthe interface layer further includes an intermetallic compoundcomprising the first metal and the second metal.
 11. The method of claim1, wherein providing the preform to the mold cavity further includescasting the preform from the one of the first metal and the second metalusing the mold cavity.
 12. The method of claim 1, wherein the preform isone of a casting, a forging, an extrusion, a stamping and a spuncomponent.
 13. The method of claim 1, wherein the preform is operativelyconfigured as a heat sink.
 14. The method of claim 6, wherein the firstportion is configured to substantially encapsulate the second portion.15. The method of claim 1, the first portion is characterized by athickness defined by the mold cavity and interface layer, and whereinthe thickness varies along the interface layer.